Method of reforming insulating film deposited on substrate with recess pattern

ABSTRACT

A method of reforming an insulating film deposited on a substrate having a recess pattern constituted by a bottom and sidewalls, includes: providing the film deposited on the substrate having the recess pattern in an evacuatable reaction chamber, wherein a property of a portion of the film deposited on the sidewalls is inferior to that of a portion of the film deposited on a top surface of the substrate; adjusting a pressure of an atmosphere of the reaction chamber to 10 Pa or less, which atmosphere is constituted by H 2  and/or He without a precursor and without a reactant; and applying RF power to the atmosphere of the pressure-adjusted reaction chamber to generate a plasma to which the film is exposed, thereby reforming the portion of the film deposited on the sidewalls to improve the property of the sidewall portion of the film.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention generally relates to a method of reforming an insulating film deposited on a substrate having a recess pattern, particularly reforming a portion of the film deposited on sidewalls of the recess pattern.

Description of the Related Art

A SiO₂ film deposited by plasma-enhanced atomic layer deposition (PEALD) is widely used in the Semiconductor manufacturing industry, since the conformality of such a film is very high, e.g., 100%, when being deposited in a trench having an aspect ratio of about 10. This film profile is important to fabrication processes such as a process of pattern transfer and target etching using spacer-defined double patterning (SDDP), wherein forming vertical spacers with accurate dimensions is important to improve resolution. However, even though a film deposited by PEALD has a high conformality, the quality of the film is not uniform throughout the film and varies depending on the geometrical location of a portion of the film. That is, a portion of the film deposited on a top surface typically has high quality, whereas a portion of the film deposited on sidewalls of a trench typically has poor quality. The poor quality of the sidewall portion of the film becomes a problem when forming a vertical spacer in the process of SDDP, for example, wherein the film deposited by PEALD on a recess pattern of a substrate is subjected to etching to remove portions of the film deposited on a top surface and on a bottom surface of the recess pattern, leaving a portion of the film deposited on sidewalls of the recess pattern, so as to form vertical spacers which are used as a mask to transfer a pattern to a template. Since the mask is subjected to etching, the sidewall portion of the film is required to have good quality such as resistance to wet etching. As such, the quality of the sidewall portion of a film is often important to patterning processes having recesses. For example, in a FinFET device, a gate oxide formed along the surfaces of trenches (including sidewalls thereof) having a high aspect ratio must have high quality. PEALD uses a plasma containing ions which have directionality (anisotropy), and thus, insufficient ion bombardment occurs on sidewalls of a trench, and as a result, the quality of a portion of the film deposited on the sidewalls is inferior to that of a portion of the film deposited on a top surface or bottom surface of the trench.

In order to improve the quality of a sidewall portion of a film, various surface-reforming processes have been developed such as those disclosed in U.S. Pat. No. 8,647,722, and No. 8,722,546. However, as miniaturization of a recess pattern becomes more prevalent, it becomes more difficult to obtain a film having satisfactory profiles, particularly, satisfactory quality of sidewall portion of the film.

Any discussion of problems and solutions in relation to the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.

SUMMARY OF THE INVENTION

Normally, deposition cycles of a film use a pressure of 100 Pa to 1,000 Pa, and when post-deposition reforming treatment is conducted to reform the film, the same pressure as in the deposition cycles is used according to conventional reforming processes. In contrast, in some embodiments of the present invention, by using an extremely low pressure such as about 1 Pa (with high RF power such as about 4 W/cm²) in post-deposition cycle reforming treatment, a sidewall portion of a film can significantly be reformed so as to improve properties of the sidewall portion of the film even when the aspect ratio of the trench is as high as 10. In some embodiments, all gas(es) used in the reforming treatment is/are an inert gas (e.g., inactive in a non-excited state) having a low atomic weight. In some embodiments, the reforming gas is constituted by or consists of H₂. The film such as that deposited by PEALD contains hydrogen as an impurity, and in non-limiting theory, by exposing the film to hydrogen ions and radicals under certain conditions (e.g., at an extremely low pressure), contaminant hydrogen can be dissociated and removed from the film, effectively from the sidewall portion, thereby converting the film to a film with a high purity. In some embodiments, He is used in combination with or in place of H₂. In some embodiments, when the pressure of the reforming treatment is 10 Pa or less, improvement on the properties of the sidewall portion (such as resistance to wet etching) becomes pronounced, and when the pressure is 2 Pa or less, the properties of the sidewall portion of the film can become equivalent to those of the top portion of the film. In non-limiting theory, by using an extremely low pressure during the reforming treatment, the mean free path of ions/radicals of small molecules can be prolonged and ions/radicals can travel through the gas phase and reach the sidewalls of a trench at an increased probability, and also, radicals having an extended life may be generated by ions, thereby reaching the sidewalls of a trench at an increased probability.

For purposes of summarizing aspects of the invention and the advantages achieved over the related art, certain objects and advantages of the invention are described in this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

Further aspects, features and advantages of this invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described with reference to the drawings of preferred embodiments which are intended to illustrate and not to limit the invention. The drawings are greatly simplified for illustrative purposes and are not necessarily to scale.

FIG. 1 is a schematic representation of a PEALD (plasma-enhanced atomic layer deposition) apparatus for depositing a dielectric film usable in an embodiment of the present invention.

FIG. 2 shows schematic cross sectional views of an insulating film (e.g., SiO₂ film) deposited by PEALD, for example, wherein (a) is a view of the film profiles before being subjected to wet etching, (b) is a view of the film profiles without reforming treatment after being subjected to wet etching, (c) is a view of the film profiles with conventional reforming treatment after being subjected to wet etching, and (d) is a view of the film profiles with reforming treatment according to an embodiment of the present invention after being subjected to wet etching.

FIG. 3 is a STEM photograph showing a cross sectional view of an insulating film without reforming treatment after being subjected to wet etching.

FIG. 4 is a STEM photograph showing a cross sectional view of an insulating film with reforming treatment according to a comparative example after being subjected to wet etching.

FIG. 5 is a STEM photograph showing a cross sectional view of an insulating film with reforming treatment according to another comparative example after being subjected to wet etching.

FIG. 6 is a STEM photograph showing a cross sectional view of an insulating film with reforming treatment according to an embodiment of the present invention after being subjected to wet etching.

FIG. 7 shows schematic illustrations of profile changes of a trench in film evaluation processes according to an embodiment of the present invention, wherein (A) illustrates a profile of the trench with an underlying layer, (B) illustrates a profile of the trench with a SiO₂ film, (C) illustrates a profile of the trench subjected to reforming treatment, and (D) illustrates a profile of the trench after wet-etching.

FIG. 8 is a graph showing the pressure dependency of wet etch rate of surface-reformed insulating films deposited on a top surface, sidewall, and bottom surface of a trench.

FIG. 9 is a graph showing the pressure dependency of wet etch rate of surface-reformed insulating films deposited on a top surface and sidewall of a trench, which films were surface-reformed with low RF power and high RF power.

FIG. 10 is a graph showing the RF power dependency of wet etch rate of surface-reformed insulating films deposited on a top surface, sidewall, and bottom surface of a trench.

FIG. 11 is a graph showing the effect of plasma treatment time of reforming treatment on thickness of insulating films on top surfaces subjected to wet etching.

FIG. 12 is a schematic representation of an apparatus conducting an extremely-low-pressure reforming treatment according to an embodiment of the present invention.

FIG. 13 shows a schematic process sequence of extremely-low-pressure surface-reforming treatment according to an embodiment of the present invention wherein a step-up line represents an ON state or an increased-quantity state whereas a step-down line represents an OFF state or a decreased-quantity state, and the height and duration of each section are not necessarily to scale.

FIG. 14 shows a schematic process sequence of a film deposition process continuously followed by extremely-low-pressure surface-reforming treatment according to an embodiment of the present invention wherein a step-up line represents an ON state wherein a step-up line represents an ON state or an increased-quantity state whereas a step-down line represents an OFF state or a decreased-quantity state, and the height and duration of each section are not necessarily to scale.

FIG. 15 shows schematic illustrations of processes to keep only a bottom portion of film in a trench or hole according to an embodiment of the present invention, wherein (A) illustrates a process of depositing a film in a trench or hole, (B) illustrates a process of reforming treatment, and (C) illustrates a process of selectively removing a sidewall portion and a top portion of the film.

FIG. 16 is a schematic representation of an application of a reformed film according to an embodiment of the present invention, which film is used in a double-gate FinFET device.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid and may be constituted by a single gas or a mixture of gases, depending on the context. Likewise, an article “a” or “an” refers to a species or a genus including multiple species, depending on the context. In this disclosure, a process gas for deposition introduced to a reaction chamber through a showerhead may be comprised of, consist essentially of, or consist of a silicon-containing precursor and an additive gas. The additive gas may include a reactant gas for oxidizing, nitriding and/or carbonizing the precursor, and an inert gas (e.g., noble gas) for exciting the precursor, when RF power is applied to the additive gas. The inert gas may be fed to a reaction chamber as a carrier gas and/or a dilution gas. Further, in some embodiments, no reactant gas is used, and only noble gas (as a carrier gas and/or a dilution gas) is used. The precursor and the additive gas can be introduced as a mixed gas or separately to a reaction space. The precursor can be introduced with a carrier gas such as a rare gas. A gas other than the process gas, i.e., a gas introduced without passing through the showerhead, may be used for, e.g., sealing the reaction space, which includes a seal gas such as a rare gas. In some embodiments, the term “precursor” refers generally to a compound that participates in the chemical reaction that produces another compound, and particularly to a compound that constitutes a film matrix or a main skeleton of a film, whereas the term “reactant” refers to a compound, other than precursors, that is used in association with a precursor and activates the precursor, modifies the precursor, or catalyzes a reaction of the precursor, wherein the reactant may provide an element (such as O, N, and/or C) to a film matrix and become a part of the film matrix, when RF power is applied. The term “inert gas” refers to a gas that is inactive when RF power (or other electromagnetic energy) is not applied but can become a plasma state to excite a precursor or reform a film when RF power (or other electromagnetic energy) is applied, but unlike a reactant, it may not become a part of or incorporated into a film matrix.

In some embodiments, “film” refers to a layer continuously extending in a direction perpendicular to a thickness direction substantially without pinholes to cover an entire target or concerned surface, or simply a layer covering a target or concerned surface. In some embodiments, “layer” refers to a structure having a certain thickness formed on a surface or a synonym of film or a non-film structure. A film or layer may be constituted by a discrete single film or layer having certain characteristics or multiple films or layers, and a boundary between adjacent films or layers may or may not be clear and may be established based on physical, chemical, and/or any other characteristics, formation processes or sequence, and/or functions or purposes of the adjacent films or layers. Further, in this disclosure, any two numbers of a variable can constitute a workable range of the variable as the workable range can be determined based on routine work, and any ranges indicated may include or exclude the endpoints. Additionally, any values of variables indicated (regardless of whether they are indicated with “about” or not) may refer to precise values or approximate values and include equivalents, and may refer to average, median, representative, majority, etc. in some embodiments. Further, in this disclosure, the terms “constituted by” and “having” refer independently to “typically or broadly comprising”, “comprising”, “consisting essentially of”, or “consisting of” in some embodiments. In this disclosure, any defined meanings do not necessarily exclude ordinary and customary meanings in some embodiments.

In the present disclosure where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation.

In all of the disclosed embodiments, any element used in an embodiment can be replaced with any elements equivalent thereto, including those explicitly, necessarily, or inherently disclosed herein, for the intended purposes. Further, the present invention can equally be applied to apparatuses and methods.

The embodiments will be explained with respect to preferred embodiments. However, the present invention is not limited to the preferred embodiments.

In an embodiment, a method of reforming an insulating film deposited on a substrate having a recess pattern constituted by a bottom and sidewalls, comprises: (i) providing the film deposited on the substrate having the recess pattern in an evacuatable reaction chamber, wherein a property of a portion of the film deposited on the sidewalls is inferior to that of a portion of the film deposited on a top surface of the substrate; (ii) adjusting a pressure of an atmosphere of the reaction chamber to 10 Pa or less, which atmosphere is constituted by H₂ and/or He without a precursor; and (iii) applying RF power to the pressure-adjusted reaction chamber to generate a plasma to which the film is exposed, thereby reforming the portion of the film deposited on the sidewalls to improve the property of the sidewall portion of the film.

In this disclosure, the insulating film provided in step (i) includes, but is not limited to, an oxide film or nitride film, which is selected from the group consisting of SiO₂, SiN, SiOC, SiCN, GeOx, GeN, AlOx, AlN, TiO₂, and TaO₂, for example. In some embodiments, the insulating film has a dielectric constant of about 1.9 to 5.0, typically about 2.1 to 3.0, preferably less than 2.5. In some embodiments, the dielectric film is formed in trenches or vias including side walls and bottom surfaces, and/or flat surfaces (top surfaces), by plasma-enhanced CVD, thermal CVD, cyclic CVD, plasma-enhanced ALD, thermal ALD, radical-enhanced ALD, or any other thin film deposition methods. Typically, the thickness of the insulating film (typically the thickness of film deposited on a top surface unless otherwise specified) is 10 nm or less (e.g., 7 nm or less, more than 1 nm) so that the surface-reforming effect can be exerted on the film substantially in its entirety. In some embodiments, by repeating the surface-reforming step (steps (ii) and (iii)) after every deposition of a film having a thickness of 10 nm or less, the total thickness of a reformed film can be more than 10 nm, e.g., in a range of about 20 nm to about 500 nm (a desired film thickness can be selected as deemed appropriate according to the application and purpose of film, etc.).

In some embodiments, step (i) comprises depositing the film in the reaction chamber by cyclic deposition, wherein the film is deposited by one cycle or multiple cycles of the cyclic deposition. That is, in the embodiments, the deposition step and the reforming step are continuously performed in the same reaction chamber. In this disclosure, “continuously” refers to without breaking a vacuum, without interruption as a timeline, without any material intervening step, without changing treatment conditions, immediately thereafter, as a next step, or without an intervening discrete physical or chemical structure between two structures other than the two structures in some embodiments. Alternatively, the deposition step can be performed in a different reaction chamber, and the substrate is transferred to another reaction chamber for the reforming step. For the purpose, a cluster type apparatus equipped with multiple reaction chambers connected to a common wafer transfer chamber can be used. In some embodiments, the cyclic deposition is plasma-enhanced atomic layer deposition (PEALD). In some embodiments, steps (i) through (iii) are repeated. In the present disclosure where conditions and/or structures are not specified for deposition of an insulating film, a skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation.

In this disclosure, a recess between adjacent vertical spacers and any other recess pattern constituted by a bottom and sidewalls are referred to as a “trench”. That is, the trench is any recess pattern including a pattern formed by vertical spacers and which has, in some embodiments, a width of about 20 nm to about 100 nm (typically about 30 nm to about 50 nm) (wherein when the trench has a length substantially the same as the width, it is referred to as a hole/via, and a diameter thereof is about 20 nm to about 100 nm), a depth of about 30 nm to about 100 nm (typically about 40 nm to about 60 nm), and an aspect ratio of about 2 to about 10 (typically about 2 to about 5). In this disclosure, the dimensions of the trench refer to those of the trench covered with a target film which is subjected to the reforming treatment, not those of the naked trench to which no film has not been deposited. The proper dimensions of the trench may vary depending on the process conditions, film compositions, intended applications, etc.

In some embodiments, the film deposited in the recess pattern has a conformality (a ratio of thickness of film deposited on sidewalls to thickness of film deposited on a top surface or on a bottom surface) of 80% to 100%, typically approximately 90% or higher. In this regard, preferably, the film is deposited by PEALD. However, typically, such film has a problem in that a property of a portion of the film deposited on the sidewalls is substantially inferior to that of a portion of the film deposited on a top surface of the substrate. In the disclosure, “substantially inferior”, “substantially different”, “substantially less” or the like may refer to a material difference or a difference recognized by a skilled artisan such as those of at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any ranges thereof in some embodiments. Also, in the disclosure, “substantially the same”, “substantially uniform”, or the like may refer to an immaterial difference or a difference recognized by a skilled artisan such as those of less than 10%, less than 5%, less than 1%, or any ranges thereof in some embodiments.

In this disclosure, the property of the film includes, but is not limited to, resistance to wet etching which can be evaluated by immersing a film in a solution of DHF (diluted hydrogen fluoride) having a dilution ratio of 1/1,000, for example.

In step (ii), the pressure of an atmosphere of the reaction chamber is adjusted to 10 Pa or less, which atmosphere is constituted by an inert gas such as H₂ and/or He without a precursor and without a reactant. As defined in this disclosure, the term “inert gas” in step (ii) refers to a gas that is inactive when RF power (or other electromagnetic energy) is not applied but can become a plasma state to excite a precursor or reform a film when RF power (or other electromagnetic energy) is applied, but unlike a reactant, it may not become a part of or incorporated into a film matrix. In step (ii), the term “precursor” refers generally to a compound that participates in the chemical reaction that produces another compound, and particularly to a compound that constitutes a film matrix or a main skeleton of a film, whereas the term “reactant” refers to a compound, other than precursors, that is used in association with a precursor and activates the precursor, modifies the precursor, or catalyzes a reaction of the precursor, wherein the reactant may provide an element (such as O, N, and/or C) to a film matrix and become a part of the film matrix, when RF power is applied. In some embodiments, the inert gas in step (ii) has an atomic weight of less than that of oxygen (16). When the molecule of the inert gas has a small diameter, and the number of molecules per unit volume is high, the mean free path of ions generated from the inert gas can be long since the mean free path can be defined as follows (simplified as a mean distance per collision):

$\frac{1}{\pi\; d^{2}n_{v}}$ wherein d is a diameter of a molecule, and n_(v) is the number of molecules per unit volume. When the mean free path of ions becomes long, the ions can travel a long distance, i.e., reaching a film deposited on sidewalls of a trench having a high aspect ratio (increasing ion bombardments on the sidewalls), and improving the properties of the film. Also, by decreasing the pressure, n_(v) is decreased, thereby prolonging the mean free path of ions. As a result, reforming of the film, particularly at the sidewall (also the bottom), deposited in a trench can effectively be performed, thereby improving substantially the properties of the film deposited on the sidewalls. In view of the above, H₂ is preferably used as the inert gas. He also can be used for similar reasons. In the deposition process, H₂ can generally be used as a reactant gas; however, in step (ii), H₂ is used as the inert gas since it is not used in association with a precursor. In non-limiting theory, in step (iii), H₂ generates a hydrogen plasma and removes contaminant hydrogen contained in the film as an impurity, thereby improving the properties of the film, particularly the sidewall portion of the film.

In some embodiments, in step (ii), the atmosphere of the reaction chamber further contains N₂ at a concentration of 1% or less (e.g., 0.05% to 0.2%, typically 0.1%), wherein N₂ is used predominantly as an inert gas, and does not substantially function as a reactant gas (see the definitions of the terms described in this disclosure). By using a small quantity of N₂, removal of contaminant hydrogen from the film can be promoted in step (iii), although it may slightly contribute to nitridization of the film. In some embodiments, in step (ii), the atmosphere contains no gas other than H₂, He, and N₂. In some embodiments, the atmosphere consists of H₂.

In step (ii), the pressure of an atmosphere of the reaction chamber is adjusted to 10 Pa or less so as to perform the reforming of film effectively. Preferably, the pressure of the atmosphere of the reaction chamber is extremely low such as 2 Pa or less, 1 Pa or less, or less than 1 Pa. The lowest pressure can be determined depending on whether a plasma is ignited, and typically, the pressure is 10⁻² Pa or higher. In some embodiments, in step (i), a pressure of an atmosphere of the reaction chamber is controlled using a dry pump connected to the reaction chamber, and in step (ii), the pressure of the atmosphere of the reaction chamber is controlled using a turbomolecular pump connected to the reaction chamber. The use of a turbomolecular pump can effectively reduce the pressure to an extremely low level. For example, the lowest pressure achieved by a dry pump may be 1 Pa, whereas the lowest pressure achieved by a turbomolecular pump may be 10⁻⁵ Pa. For deposition, a dry pump is normally used because the dry pump has a high capacity of evacuation. If the exhaust rate is set high, and the inert gas such as H₂ is fed to the reaction chamber at a flow rate of approximately 3 sccm, for example, the sole use of a dry pump may be able to reduce the pressure to a desired level.

In some embodiments, between steps (i) and (ii), the reaction chamber is evacuated to reduce the pressure to less than the pressure used in step (ii), i.e., the pressure of the reaction chamber is reduced to nearly zero before setting the atmosphere of the reaction chamber in step (ii), and then, in step (ii), the inert gas is introduced to set the pressure at a desired level. For example, after step (i) before step (ii), the pressure is reduced to 10⁻² Pa, and then, is increased to 1 Pa for step (ii). By evacuating the reaction chamber to reduce the pressure to less than the pressure used in step (ii) between steps (i) and (ii), residual gas remaining in the reaction chamber can effectively be removed before step (ii).

In step (iii), RF power is applied to the atmosphere of the pressure-adjusted reaction chamber to generate a plasma to which the film is exposed, thereby reforming the portion of the film deposited on the sidewalls to improve the property of the sidewall portion of the film. In some embodiments, in step (iii), RF power is applied at a power of 2 W/cm² or higher (e.g., 3, 4, 5, 6, 7, 8, 9, or 10 W/cm² or a value between any two numbers of the foregoing) relative to the top surface of the substrate. The frequency of RF power is in a range of 1 to 100 MHz, preferably 13.5 to 60 MHz, and in some embodiments, the frequency of RF power for the reforming process is higher than that used for the deposition process.

When the pressure in step (ii) is higher, RF power in step (iii) may need to be higher to achieve desired reforming effects. For example, when the pressure is less than 2 Pa, RF power is approximately 2 to 6 W/cm² whereas when the pressure is 2 Pa to 10 Pa, RF power is approximately 6 to 10 W/cm². If RF power is too low, no plasma is ignited or no sufficient improvement on properties of a film can be obtained, whereas if RF power is too high, even though sufficient improvement on properties of a film on sidewalls can be obtained, a film on a top surface will be damaged. Thus, if improvement on properties of a film mainly on sidewalls is the goal, relatively high RF power can be used. In some embodiments, in step (iii), the reforming the sidewall portion of the film is accomplished by removing hydrogen contained in the film as an impurity using the plasma, thereby improving the properties of the sidewall portion of the film. Typically, the film contains hydrogen as an impurity, and by removing the hydrogen, the film properties can be improved. For example, the concentration of hydrogen in the film can be reduced by step (iii) from approximately 7×10²¹ atms/cm³ to approximately 2×10²¹ atms/cm³ (in some embodiments, the hydrogen concentration in the film is reduced by 50% to 90% or 70% to 80% by the reforming treatment). In some embodiments, step (iii) is conducted until the property of the sidewall portion of the film is improved to be substantially equivalent the property of a portion of the film deposited on the bottom of the recess pattern or a top surface of the substrate. In some embodiments, in step (iii), RF power is applied to an upper electrode which is capacitively coupled with a lower electrode on which the substrate is placed.

In some embodiments, in step (i), a portion of the film deposited on the bottom of the recess pattern is thicker than the portion at the sidewalls of the recess pattern and the portion at the top surface of the substrate. According to conventional reforming treatment, the properties of the top portion of the film can be improved, whereas those of the sidewall portion and the bottom portion cannot be improved as much as that of the top portion. However, through step (iii), not only the property of the sidewall portion of the film but also those of the bottom portion can be improved. Thus, some embodiments are modified so as to use the bottom portion of the film, rather than the sidewall portion of the film. In semiconductor manufacturing processes, controlling the profile of film deposited in a recess pattern is very important. For example, when etching a recess pattern having a high aspect ratio, even when a bottom portion of the film is intended to be maintained, since the bottom portion of the film is easily etched, the bottom portion of the film may undesirably be removed. After forming a trench or via hole having a high aspect ratio, in some cases, there is a demand to form an etch stop layer (using, e.g., a SiO or SiN film) only on the bottom of the trench or via hole.

The embodiments will be explained with respect to the drawings. However, the present invention is not limited to the drawings.

FIG. 2 shows schematic cross sectional views of an insulating film (e.g., SiO₂ film) deposited by PEALD, for example, wherein (a) is a view of the film profile before being subjected to wet etching, (b) is a view of the film profile without reforming treatment after being subjected to wet etching, (c) is a view of the film profile with conventional reforming treatment after being subjected to wet etching, and (d) is a view of the film profile with reforming treatment according to an embodiment of the present invention after being subjected to wet etching.

In (a), a conformal film 32 is deposited by PEALD, for example, on a surface of a substrate 31 having a trench 30. The conformal film 32 has a conformality of approximately 100%. In (b), the conformal film 32 is subjected to wet etching without surface-reforming treatment. Since the conformal film 32 is not densified and also contains hydrogen as an impurity, the film is etched rather uniformly at a high wet etch rate, resulting in an etched film profile 33 having a thin film thickness and a relatively high conformality (60% to 80%). In (c), the conformal film 32 is subjected to wet etching after conducting conventional surface-reforming treatment (e.g., using Ar/O₂ gas at a pressure of 100 Pa, for example). Although the conformal film 32 is densified on a top surface and hydrogen is removed therefrom as an impurity by the surface-reforming treatment, the conformal film 32 is not sufficiently densified on sidewalls and hydrogen is not removed therefrom, and thus, the film deposited on the top surface can have good resistance to wet etching, but the film on the sidewalls does not and is etched at a high wet etch rate, resulting in an etched film profile 34 having a thin film thickness on the sidewalls and a thick film thickness on the top surface and a relatively low conformality (40% to 60%). In (d), the conformal film 32 is subjected to wet etching after conducting surface-reforming treatment according to an embodiment of the present invention (e.g., using H₂ gas at a pressure of 1 Pa, for example). Since the conformal film 32 is densified not only on the top surface but also on the sidewalls, and hydrogen is removed therefrom as an impurity by the surface-reforming treatment, the conformal film 32 is sufficiently densified not only on the top surface but also on the sidewalls and hydrogen is removed therefrom, and thus, the film deposited on the top surface and the sidewalls can have good resistance to wet etching and is etched at a low wet etch rate, resulting in an etched film profile 35 having a thick film thickness along the entire surface of the trench and a high conformality (e.g., 90% to 110%).

FIG. 13 shows a schematic process sequence of extremely-low-pressure surface-reforming treatment according to an embodiment of the present invention wherein a step-up line represents an ON state or an increased-quantity state whereas a step-down line represents an OFF state or a decreased-quantity state, and the height and duration of each section are not necessarily to scale. In the sequence illustrated in FIG. 13, step a is a transition step where the reaction chamber accommodating a Si wafer (having trenches) is fully evacuated to remove substantially all residual gas remaining in the reaction chamber from a deposition process or the like. In step a, no gas is fed to the reaction chamber, no RF power is applied to the reaction chamber, and the pressure of the reaction chamber is reduced to substantially a fully vacuumed level, e.g., less than 1 Pa (e.g., 10⁻² Pa or less). Next, the surface-reforming treatment begins in step b which is a stabilizing step where a reforming gas is fed to the reaction chamber at a low flow rate (e.g., less than 10 sccm) without applying RF power, while adjusting the pressure to a desired extremely low level such as 1 Pa, so as to establish an atmosphere of the reaction chamber for surface-reforming. The reforming gas is an inert gas such as H₂ and/or He. In step c, RF power is applied to the atmosphere of the reaction chamber to conduct surface-reforming by a plasma while maintaining the extremely low pressure. In step d which is a stabilizing step, application of RF power is stopped while maintaining the reforming gas flow and the extremely low pressure, wherein the reforming gas flow can be gradually reduced and stopped so as to suppress generation of particles. In step e which is a transition step, the reaction chamber is fully evacuated without feeding the reforming gas. In some embodiments, in steps a and e, the pressure of the reaction chamber need not be reduced to substantially a fully vacuumed level, but the pressure can be the same as that in steps b to d.

FIG. 14 shows a schematic process sequence of a film deposition process continuously followed by extremely-low-pressure reforming treatment according to an embodiment of the present invention wherein a step-up line represents an ON state wherein a step-up line represents an ON state or an increased-quantity state whereas a step-down line represents an OFF state or a decreased-quantity state, and the height and duration of each section are not necessarily to scale. In this process sequence, the deposition process and the reforming process are conducted continuously in the same reaction chamber accommodating a Si wafer having trenches. Steps A to D constitute one cycle of PEALD. In step A, a precursor (such as alkylaminosilane) is fed in a pulse to the reaction chamber to chemisorb a precursor on a surface of the wafer while continuously feeding a reactant gas (e.g., O₂) and dilution/carrier gas (e.g., Ar) through steps A to D, wherein the pressure of the reaction chamber is set at a deposition pressure such as 200 Pa using a dry pump (DP) through steps A to D. In step C, RF power is applied to the reaction chamber to expose the precursor-adsorbed wafer to a plasma of the reaction gas so as to form a monolayer on the surface of the wafer including the trenches. Steps B and D are purging steps, wherein the continuous flows of the reactant gas and the dilution/carrier gas function as purging gases. The one cycle is repeated until a desired thickness of film is obtained on the wafer. The desired thickness of film may be 10 nm or less because the surface-reforming process may reform a film from the top surface to a portion approximately 10 nm or less deep from the surface, if the entire film is intended to be reformed. By repeating the deposition process and the reforming process, a film fully reformed can be formed at a desired final thickness.

After the deposition process is complete, a reforming process begins. Step P is a first transition steps where the reaction gas flow is completely stopped, and the dilution/carrier gas flow is gradually stopped so as to suppress generation of particles, and the pressure of the reaction chamber is reduced using the dry pump. Step Q is a second transition step where the dilution/carrier gas flow is completely stopped, and the vacuum pump is switched from the dry pump (DP) to a turbomolecular pump (TMP) so as to reduce the pressure to substantially a fully vacuumed level, e.g., less than 1 Pa (e.g., 10⁻² Pa or less) so that the reaction chamber is fully evacuated to remove substantially all residual gas remaining in the reaction chamber from the deposition process. In step Q, no gas is fed to the reaction chamber, and no RF power is applied to the reaction chamber. Next, the surface-reforming treatment begins in step R which is a stabilizing step where a reforming gas is fed to the reaction chamber at a low flow rate (e.g., less than 10 sccm) without applying RF power, while adjusting the pressure to a desired extremely low level such as 1 Pa using the TMP, so as to establish an atmosphere of the reaction chamber for surface-reforming. The reforming gas is an inert gas such as H₂ and/or He. In step S, RF power is applied to the atmosphere of the reaction chamber to conduct surface-reforming by a plasma while maintaining the extremely low pressure. In step T which is a stabilizing step, application of RF power is stopped while maintaining the reforming gas flow and the extremely low pressure, wherein the reforming gas flow can be gradually reduced and stopped so as to suppress generation of particles. In step U which is a first transition step, the reaction chamber is fully evacuated without feeding the reforming gas, and flow of the dilution/carrier gas (without the precursor) starts and gradually increases so as to suppress generation of particles, while the pressure is also gradually increased. In step V which is a second transition step, the dilution/carrier gas flows constantly, and the vacuum pump is switched from the TMP to the DP so as to increase the pressure for the next deposition process (e.g., 200 Pa).

The process cycle can be performed using any suitable apparatus including an apparatus illustrated in FIG. 1, for example. FIG. 1 is a schematic view of a PEALD apparatus, desirably in conjunction with controls programmed to conduct the sequences described below, usable in some embodiments of the present invention. In this figure, by providing a pair of electrically conductive flat-plate electrodes 4, 2 in parallel and facing each other in the interior 11 (reaction zone) of a reaction chamber 3, applying HRF power (13.56 MHz or 27 MHz) 25 to one side, and electrically grounding the other side 12, a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 2 (the lower electrode), and a temperature of a substrate 1 placed thereon is kept constant at a given temperature. The upper electrode 4 serves as a shower plate as well, and reactant gas and/or dilution gas, if any, and precursor gas are introduced into the reaction chamber 3 through a gas line 21 and a gas line 22, respectively, and through the shower plate 4. Additionally, in the reaction chamber 3, a circular duct 13 with an exhaust line 7 is provided, through which gas in the interior 11 of the reaction chamber 3 is exhausted. Additionally, a transfer chamber 5 disposed below the reaction chamber 3 is provided with a seal gas line 24 to introduce seal gas into the interior 11 of the reaction chamber 3 via the interior 16 (transfer zone) of the transfer chamber 5 wherein a separation plate 14 for separating the reaction zone and the transfer zone is provided (a gate valve through which a wafer is transferred into or from the transfer chamber 5 is omitted from this figure). The transfer chamber is also provided with an exhaust line 6. In some embodiments, the deposition of multi-element film and reforming treatment are performed in the same reaction space, so that all the steps can continuously be conducted without exposing the substrate to air or other oxygen-containing atmosphere.

The reforming process can be conducted in a different reaction chamber or in the same reaction chamber as the deposition process. FIG. 12 is a schematic representation of an apparatus conducting an extremely-low-pressure reforming treatment according to an embodiment of the present invention, which can also be used for the deposition process (when the deposition process uses RF power which is different from that used for the reforming process, the apparatus needs to be equipped with two RF power sources for different frequencies). In this figure, by providing a pair of electrically conductive flat-plate electrodes 92, 93 in parallel and facing each other in the interior (reaction zone) of a reaction chamber 91, applying HRF power (1 MHz to 100 MHz, typically 60 MHz) from an RF power source 95 to the upper electrode 93, and electrically grounding the lower electrode 92, a plasma is excited between the electrodes. A temperature regulator is provided in a lower stage 92 (the lower electrode), and a temperature of a substrate 94 placed thereon is kept constant at a given temperature. The upper electrode 93 serves as a shower plate as well, and reforming gas or gases are introduced into the reaction chamber 91 through gas lines provided with mass flow controllers 97, 98, respectively, and merged into a gas line with a valve 96, through the shower plate 93. Further, the reaction chamber 91 is equipped with two exhaust systems. One exhaust system is provided with a dry pump 105 connected to the reaction chamber 91 via a throttle valve 102, and the other exhaust system is provided with a turbomolecular pump 104 (with an RP pump filter 103) connected to the reaction chamber 91 via a throttle valve 101. The throttle valve 101 and the turbomolecular pump 104 and the throttle valve 102 and the dry pump 105 are controlled by one or more controller(s) (not shown) so as to switch from one to another, according to the process recipe.

A skilled artisan will appreciate that the apparatus includes one or more controller(s) (not shown) programmed or otherwise configured to cause the deposition and reactor cleaning processes described elsewhere herein to be conducted. The controller(s) are communicated with the various power sources, heating systems, pumps, robotics and gas flow controllers or valves of the reactor, as will be appreciated by the skilled artisan.

In some embodiments, a dual chamber reactor (two sections or compartments for processing wafers disposed closely to each other) can be used, wherein a reactant gas and a noble gas can be supplied through a shared line whereas a precursor gas is supplied through unshared lines.

FIG. 15 shows another aspect of the present invention, which shows schematic illustrations of processes to keep only a bottom portion of film in a trench or hole, wherein (A) illustrates a process of depositing a film in a trench or hole, (B) illustrates a process of reforming treatment, and (C) illustrates a process of selectively removing a sidewall portion and a top portion of the film. Through the reforming treatment process, not only the property of the sidewall portion of the film but also those of the bottom portion can be improved. Thus, some embodiments can be modified so as to use the bottom portion of the film, rather than the sidewall portion of the film. In (A), a film 82 is deposited in a trench or hole of a substrate 81, wherein a bottom portion of the film is much thicker than a sidewall portion and a top portion of the film. Such a film profile can be achieved by using gap-fill CVD method or reflow method which is known in the art. In (B), reforming treatment is conducted so that the film is exposed to a plasma at a low pressure, thereby reforming the film from the surface toward the inside in a thickness direction (a region 83 with hatching is a reformed portion). By the reforming treatment, not only the sidewall portion of the film but also the bottom portion (also the top portion) of the film can be reformed. In (C), the reformed film is subjected to dry etching or wet etching so as to remove the sidewall and top portions of the film, selectively leaving the bottom portion 84 of the film. The bottom portion 84 of the film can be used as an etch stop layer, etc.

FIG. 16 is a schematic representation of an application of a reformed film according to an embodiment of the present invention, which film is used in a double-gate FinFET device which has a configuration wherein a silicon substrate (Fin) 93 with trenches (having a high-aspect ratio) has an oxide layer 91 (SiO₂) at the bottoms of the trenches, and a gate is formed in the trenches, wherein the surfaces of the trenches are covered with a gate oxide 94 (SiO₂), and a metal gate 92 is formed thereon. The gate oxide requires high quality in order to properly function as a gate. By using a reformed film according to some embodiments as the gate oxide 94, a high quality FinFET device can be obtained.

In some embodiments, the reforming process may be conducted under the conditions shown in Table 1 below.

TABLE 1 (numbers are approximate) Conditions for Reforming Process Substrate temperature 0 to 400° C. (preferably 50 to 300° C.) Electrode gap (a thickness of a 5 to 100 mm (preferably 10 to 80 mm) substrate is about 0.7 mm) Pressure during steps R to T in FIG. 14 10⁻³ to 10 Pa (preferably 10⁻² to 2 Pa) Flow rate of H₂ At least one of them 0 to 200 sccm (preferably 10 to 50 sccm) Flow rate of He is not zero 0 to 200 sccm (preferably 10 to 50 sccm) Flow rate of N₂ 0 to 1 sccm (preferably 0 to 0.5 sccm); less than 1% (preferably less than 0.2%) of the reforming gas RF power frequency 1 to 100 MHz, preferably 13.5 to 60 MHz RF power density 1.5 to 15 W/cm² (preferably 2.0 to 6.0 W/cm² for a pressure of 10⁻² to 2 Pa; preferably 6.0 to 10.0 W/cm² for a pressure of 2 to 10 Pa) Duration of step P in FIG. 14 3 to 10 sec. (preferably 3 to 5 sec.) Duration of step Q in FIG. 14 3 to 20 sec. (preferably 3 to 5 sec.) Duration of step R in FIG. 14 3 to 5 sec. (preferably 3 to 5 sec.) Duration of step S in FIG. 14 10 to 600 sec. (preferably 10 to 300 sec.) Duration of step T in FIG. 14 0 to 20 sec. (preferably 0 to 5 sec.) Duration of step U in FIG. 14 2 to 30 sec. (preferably 5 to 10 sec.) Duration of step V in FIG. 14 3 to 30 sec. (preferably 3 to 10 sec.) Thickness of Film subjected to the 0.1 to 20 nm (preferably 0.1 to 10 nm) on top reforming treatment surface Conformality of Film subjected to the 0.5 to 80 (preferably 2 to 20) reforming treatment

The above-indicated RF power is expressed as applied wattage (W) per cm² of an apparent top surface of a substrate (assuming that the top surface is continuous and ignoring the areas of trenches) which can apply to a wafer having a different diameter such as 100 mm or 450 mm.

In some embodiments, when H₂ and He are mixed, a ratio of H₂ flow to He flow is 5 to 200, preferably 10 to 50. In some embodiments, when only a top portion of a target film (e.g., a top portion having a depth of 10 nm or less) is required to be reformed, the target film can have a thickness of more than 10 nm, e.g., 50 nm to 500 nm). Typically, the reforming process is repeated after every deposition process until a desired thickness of a film is obtained. For example, when a growth rate of a film per cycle of PEALD is about 0.1 nm, the cycle of PEALD is repeated 100 times so as to obtain a first layer having a thickness of about 10 nm, and then, the reforming process is conducted; thereafter, the cycle of PEALD is again repeated 100 times so as to deposit a second layer having a thickness of about 10 nm, followed by the reforming process; and the above process is repeated until the total thickness of a film reaches about 50 nm, i.e., repeated five times (five layers).

The reforming process can be used in various applications, including spacer-defined double patterning (SDDP), wherein a silicon oxide film reformed according any of the disclosed embodiments or equivalents thereto can be used as a vertical spacer.

The surface-reformed insulating film may be resistant to not only HF, HCl, and TMAH wet etch, but also e.g. to BCl₃, BCl₃/Ar, dry etch; On the other hand, the surface-reformed insulating film may be sensitive to oxidation, a combination of wet etch chemistry alternating oxidizing and HF (common in semiconductor processing), or dry etch based on oxygen or CF₄, for example, and thus, the surface-reformed insulating film can effectively be stripped according to the process recipe and application.

The present invention is further explained with reference to working examples below. However, the examples are not intended to limit the present invention. In the examples where conditions and/or structures are not specified, the skilled artisan in the art can readily provide such conditions and/or structures, in view of the present disclosure, as a matter of routine experimentation. Also, the numbers applied in the specific examples can be modified by a range of at least ±50% in some embodiments, and the numbers are approximate.

EXAMPLES Example 1

A substrate (having a diameter of 100 mm and a thickness of 0.7 mm) having a SiO₂ film deposited by PEALD was provided wherein the substrate had trenches with an opening width of approximately 30 nm and a depth of approximately 300 nm (an aspect ratio of 10). The SiO₂ film was formed on an underlying layer (SiN) by PECVD with a thickness of about 15 nm on the substrate, which underlying layer was formed in order to adjust the shapes of the trenches before depositing the SiO₂ film wherein the trenches of the substrate with the underlying film had an opening width of approximately 60 nm and a depth of approximately 300 nm (an aspect ratio of 5). Reforming treatment was conducted on the substrate using a sequence illustrated in FIG. 13 under the conditions shown in Table 2 below using the apparatus illustrated in FIG. 12, wherein the film was deposited using the apparatus illustrated in FIG. 1 which was hermetically connected to the apparatus for reforming process via a wafer handling chamber so that the substrate could continuously be transferred from the deposition chamber to the reforming chamber without breaking a vacuum state. Multiple films were treated under partially different conditions of reforming treatment for analysis (see Table 3). The reformed film was subjected to wet etching (dipped in a solution of DHF 1000:1 for 10 minutes) and analyzed for resistance to wet etching. The results are shown in Table 3 below.

FIG. 7 shows schematic illustrations of the profile changes of the trench in the above steps, wherein (A) illustrates the profile of the trench with the underlying layer 71, (B) illustrates the profile of the trench with the SiO₂ film 72, (C) illustrates the profile of the trench with the SiO₂ film 72′ subjected to the reforming treatment, and (D) illustrates the profile of the trench the SiO₂ film 72″ after the wet-etching. “ΔTop”, “ΔSide”, and “ΔBtm” in Table 3 are illustrated in (D) of FIG. 7, i.e., the difference between the thickness of the SiO₂ film after the reforming treatment as shown in (C) and the thickness of the SiO₂ film after the wet etching at the top surface (“ΔTop”), at the sidewall (“ΔSide”), and at the bottom (“ΔBtm”).

TABLE 2 (numbers are approximate) Conditions for Reforming Process Substrate temperature No heating (room temperature) Electrode gap 80 mm Pressure during steps b to d in FIG. 13 See Table 3 (using TMP) Flow rate of reforming gas See Table 3 RF power frequency 60 MHz RF power density 2.5 W/cm² Duration of step a in FIG. 13 120 sec. Duration of step b in FIG. 13 60 sec. Duration of step c in FIG. 13 300 sec. Duration of step d in FIG. 13 20 sec. Duration of step e in FIG. 13 30 sec.

TABLE 3 (numbers are approximate) No Comparative reforming reforming treatment Reforming treatment Comp. Comp. treatment Comp. Ex. 1 Ex. 2 Ex. 3 Example 1 Reforming gas — Ar/O₂ H₂ H₂ Flow rate — 180/20 sccm 200 sccm 25 sccm Pressure — 100 Pa 100 Pa 1 Pa Film profile (after See FIG. 3 See FIG. 4 See FIG. 5 See FIG. 6 wet etching) Etched Δ Top  Δ 9 nm Δ 2 nm Δ 2 nm Δ 1 nm thickness Δ Side Δ 11 nm Δ 7 nm Δ 8 nm Δ 1 nm Δ Btm Δ 10 nm Δ 3 nm Δ 6 nm Δ 2 nm

In Comparative Examples 2 and 3 and Examples 1 and 2, in steps a and e in FIG. 13, the pressure was reduced to about 10⁻³ Pa (which was substantially equivalent to a base pressure) In Table 3, the Etched amount is an approximate or averaged amount. As shown in Table 3, by conducting the extremely low pressure reforming process (with a H₂ plasma) in Example 1, all the portions including the top portion, sidewall portion, and bottom portion of the film exhibited high resistance to wet etching. When conducting the comparative reforming process at a conventional pressure (100 Pa) with a H₂ plasma in Comparative Example 2, the reforming effect manifested mainly at the top portion, and least at the sidewall portion. Further, when conducting the comparative reforming process at a conventional pressure (100 Pa) with an Ar/O₂ plasma in Comparative Example 1, the reforming effect manifested mainly at the top portion, and least at the sidewall portion, in a manner similar to that in Comparative Example 2. Also, a H₂ plasma was highly effective to reform the film as shown in Example 1 at an extremely low pressure; however, when the conventional pressure (100 Pa) was used, a H₂ plasma did not show any advantageous effect on resistance to wet etching as compared with an Ar/O₂ plasma as shown in Comparative Examples 2 and 3.

FIG. 3 is a STEM photograph showing a cross sectional view of the insulating film without reforming treatment after being subjected to wet etching in Comparative Example 1. FIG. 4 is a STEM photograph showing a cross sectional view of the insulating film with reforming treatment according to Comparative Example 2 after being subjected to wet etching. FIG. 5 is a STEM photograph showing a cross sectional view of the insulating film with reforming treatment according to Comparative Example 1 after being subjected to wet etching. FIG. 6 is a STEM photograph showing a cross sectional view of the insulating film with reforming treatment according to Example 1 after being subjected to wet etching.

Example 2

Substrates with insulating films (with an aspect ratio of 10) were provided as described in Example 1 and were reformed under the conditions used in Example 1 (a pressure of 1 Pa) except that the reforming gas was changed as shown in Table 4 below, to determine resistance to wet etching at the sidewalls of trenches.

TABLE 4 (numbers are approximate) Reforming gas ΔSide - Etched thickness (nm) Example 2 H₂ 2 Comp. Ex. 3 N₂ 5 Comp. Ex. 4 O₂ 8 Comp. Ex. 5 Ar 8

As shown in Table 4, when using H₂ gas, the resistance to wet etching was significantly improved in Example 2, as compared with the use of N₂ (Comparative Example 3), O₂ (Comparative Example 4), and Ar (Comparative Example 5).

Further, in Example 2, the concentration of hydrogen atoms in the film before the reforming treatment was 7×10²¹ atms/cm³, and the concentration of hydrogen atoms in the film after the reforming treatment was reduced to 2×10²¹ atms/cm³ (which was determined using X-ray fluorescence analysis).

Example 3

A substrate (having a diameter of 100 mm and a thickness of 0.7 mm) having a SiO₂ film deposited by PEALD was provided wherein the substrate had trenches with a width of approximately 30 nm and a depth of approximately 300 nm (with an aspect ratio of 10). The SiO₂ film was formed by PEALD with a thickness of about 7 nm on the substrate and a conformality of about 100%. Reforming treatment was conducted on the substrate using a sequence illustrated in FIG. 13 under the conditions shown in Table 5 below using the apparatus illustrated in FIG. 12. Multiple films were treated under partially different conditions of reforming treatment for analysis (see FIG. 8). The reformed film was subjected to wet etching (dipped in a solution of DHF 1000:1 for 10 minutes) and analyzed for resistance to wet etching. The results are shown in FIG. 8.

TABLE 5 (numbers are approximate) Conditions for Reforming Process Substrate temperature No heating (room temperature) Electrode gap 80 mm Pressure during steps b to d in FIG. 13 See FIG. 8 (using TMP) Flow rate of H₂ 10~200 sccm RF power frequency 60 MHz RF power density 2.5 W/cm² (200 W) Duration of step a in FIG. 13 120 sec. Duration of step b in FIG. 13 60 sec. Duration of step c in FIG. 13 300 sec. Duration of step d in FIG. 13 20 sec. Duration of step e in FIG. 13 30 sec.

FIG. 8 is a graph showing the pressure dependency of wet etch rate of surface-reformed insulating films deposited on a top surface, sidewall, and bottom surface of a trench. As shown in FIG. 8, when the pressure was less than 10 Pa, the reforming effect on the resistance to wet etching of the sidewall portion of the film began to show, and when the pressure was as low as 2 Pa or less, the sidewall portion of the film was significantly reformed and the resistance to wet etching of the sidewall portion of the film became substantially equivalent to those of the top portion and the bottom portion of the film.

Example 4

Substrates with insulating films were provided and subjected to the reforming treatment under the conditions described in Example 3 except that RF power varied as shown in FIG. 9. FIG. 9 is a graph showing the pressure dependency of wet etch rate of surface-reformed insulating films deposited on a top surface and sidewall of the trench, which films were surface-reformed with low RF power (200 W; 2.55 W/cm²) and high RF power (500 W; 6.37 W/cm²). As shown in FIG. 9, when RF power was 200 W, the same pressure dependency of the property of wet etch resistance as in Example 3 was observed. However, when RF power was 500 W, regardless of the pressure, the top portion of the film showed higher wet etch rates than the sidewall portion of the film, indicating that the top portion appeared to have undertaken damage by a plasma. However, the sidewall portion of the film showed low wet etch rates even when the pressure was 10 Pa, indicating that the reforming effect on the resistance to wet etching of the sidewall portion of the film began to manifest at a pressure of 10 Pa when RF power was high. Thus, if reforming is intended to be performed only for a sidewall portion of a film, slightly higher pressure (e.g., 2 to 10 Pa) can be used in combination with high RF power (e.g., 6 to 10 W/cm²).

Example 5

Substrates with insulating films were provided and subjected to the reforming treatment under the conditions described in Example 3 except that the pressure was 1 Pa, and RF power varied as shown in FIG. 10. FIG. 10 is a graph showing the RF power dependency of wet etch rate of surface-reformed insulating films deposited on a top surface, sidewall, and bottom surface of the trench. As shown in FIG. 10, when RF power was 100 W (1.27 W/cm²), the reforming effect on the resistance to wet etching of the sidewall portion of the film did not manifest, whereas when RF power was 200 W (2.55 W/cm²) or higher, the reforming effect on the resistance to wet etching of the sidewall portion of the film was significant. However, when RF power was 500 W (6.37 W/cm²) or higher, the reforming effect on the resistance to wet etching of the top portion of the film did not manifest. In some embodiments, for 300-mm substrates with a distance between electrodes of shorter than 80 mm such as 5 to 20 mm, good reforming effect can be obtained when RF power is in a range of 700 to 7,000 W (about 1 W/cm² to 10 W/cm²). Considering that the mean free path of hydrogen ions is about 10 mm, when the distance between electrodes is in a range of 5 to 20 mm, due to increased influence of hydrogen ion bombardment, the RF power level effective to perform desired reforming treatment may be changed with reference to RF power used when the distance between electrodes is greater, such as 80 mm.

Example 6

Substrates with insulating films were provided and subjected to the reforming treatment under the conditions described in Example 3 except that the pressure was 1 Pa, and RF power was 200 W (2.55 W/cm²), and the duration of step c in FIG. 13 varied as shown in FIG. 11. FIG. 11 is a graph showing the effect of plasma treatment time of reforming treatment on thickness of insulating films on the top surfaces subjected to wet etching. As shown in FIG. 11, when the plasma treatment time was 3 minutes, the reforming effect on the resistance to wet etching of the film reached deeper in the film than when the plasma treatment time was 1 minute, indicating that the depth of the reformed portion of the film depended on the plasma treatment time. If the reforming effect reaches a portion 7 nm deep from a surface, the reforming can be accomplished in a shorter period of time when a film is thin. If the thickness of the film is about 2 nm, the plasma treatment time of 20 seconds can reform the film to provide properties which are geometrically uniform.

Example 7 (Prophetic)

On a substrate (having a diameter of 300 mm and a thickness of 0.7 mm), a SiO₂ film is deposited by PEALD using a sequence illustrated in FIG. 14 under the conditions shown in Table 6 below using the apparatus illustrated in FIG. 1 except that the apparatus is equipped with a turbomolecular pump as illustrated in FIG. 12. After 100 cycles of PEALD, reforming treatment is conducted on the substrate using a sequence illustrated in FIG. 14 under the conditions shown in Table 6 below using the same apparatus. The reformed film is subjected to wet etching (dipped in a solution of DHF 1000:1 for 10 minutes) and analyzed for resistance to wet etching. While depositing the film, the dry pump is used because a large amount of gases is fed to the chamber and discharged from the chamber. Before the reforming process begins, the dry pump line is closed and the turbomolecular pump line opens. The switching of the pumps requires time, and thus, alternatively, by increasing the evacuation speed of the dry pump and decreasing the reforming gas flow rate (e.g., 3 sccm), the extremely low pressure can be realized without using the turbomolecular pump, so as to eliminate the time for switching the pumps and to shorten the overall process duration. As a result, it will be confirmed that the sidewall portion of the film has as good resistance to wet etching as does the top portion of the film.

TABLE 6 (numbers are approximate) Conditions for Deposition Process and Reforming Process Deposition Process Substrate temperature 300° C. Electrode gap 8.5 mm Pressure 200 Pa Carrier/Dilution gas Ar Flow rate of carrier/dilution gas (continuous) 1000 sccm Precursor BDEAS Flow rate of precursor 5 sccm RF power (13.56 MHz) for a 300-mm wafer 100 W Duration of step A in FIG. 14 0.3 sec. Duration of step B in FIG. 14 0.8 sec. Duration of step C in FIG. 14 1.0 sec. Duration of step D in FIG. 14 0.1 sec. Number of cycles 100 Thickness of film 5 nm Reforming Process Substrate temperature 300° C. Electrode gap 8.5 mm Pressure during steps R to T in FIG. 14 1 Pa (using TMP) Pressure during steps Q and U in FIG. 14 10⁻² Pa (using TMP) Flow rate of H₂ 25 sccm RF power frequency 13.56 MHz RF power 2,000 W Duration of step P in FIG. 14 3 sec. Duration of step Q in FIG. 14 5 sec. Duration of step R in FIG. 14 2 sec. Duration of step S in FIG. 14 60 sec. Duration of step T in FIG. 14 5 sec. Duration of step U in FIG. 14 5 sec. Duration of step V in FIG. 14 5 sec. Number of combined cycles 3 (i.e., the total thickness of the film was 15 nm)

Example 8 (Prophetic)

In this example, a SiN film is deposited by PECVD, transferred to another chamber for reforming treatment (atmospheric exposure), and then subjected to reforming treatment using a H₂ plasma.

A substrate having a diameter of 300 mm with trenches each having an opening width of 50 nm and a depth of 300 nm is provided. The substrate is loaded in a reaction chamber for deposition, and a SiN film having a thickness of 15 nm is deposited on the substrate in the reaction chamber by PECVD using an RF power of 500 W at 350° C. using SiH₄ and NH₃ as a process gas. The substrate with the SiN film is then exposed to the atmosphere and transferred to a reaction chamber for plasma treatment which is evacuatable to a desired low pressure using a turbomolecular pump and is equipped with parallel plate electrodes. A susceptor is controlled at a temperature of 150° C., and a pressure of the reaction chamber is controlled at 1 Pa using H₂ flowing at a rate of 25 sccm, and RF power (13.56 MHz) of 2 kW is applied to the electrodes for 3 minutes, thereby exposing the film to a H₂ plasma. The resultant SiN film on the substrate has a decreased hydrogen content as compared with that of the SiN film as deposited, thereby rendering the film high-quality, particularly at the sidewalls of the trenches. In the above, the reaction chamber for deposition and the reaction chamber for plasma treatment both have configurations corresponding to those illustrated in FIG. 1, and exhausting the former chamber is conducted using a dry pump whereas exhausting the latter chamber is conducted using a turbomolecular pump.

Example 9 (Prophetic)

In this example, a SiO₂ film is deposited by PEALD, transferred to another chamber for reforming treatment (without atmospheric exposure), and then subjected to reforming treatment using a He/H₂ plasma.

A substrate having a diameter of 300 mm with holes each having an opening diameter of 30 nm and a depth of 300 nm is provided. The substrate is loaded in a reaction chamber for deposition, and a SiO₂ film having a thickness of 5 nm is deposited on the substrate in the reaction chamber by PEALD at a substrate temperature of 300° C. using BDMAS (bisdimethylaminosilane) and an O₂ plasma. The substrate with the SiO₂ film is then transferred to a reaction chamber for plasma treatment (while continuously maintaining a vacuum without atmospheric exposure) which is evacuatable to a desired low pressure using a turbomolecular pump and is equipped with parallel plate electrodes. A susceptor is controlled at a temperature of 300° C., and a pressure of the reaction chamber is controlled at 1 Pa using He flowing at a rate of 20 sccm and H₂ flowing at a rate of 25 sccm, and RF power (13.56 MHz) of 2 kW is applied to the electrodes for 3 minutes, thereby exposing the film to a He/H₂ plasma. The resultant SiO₂ film on the substrate has high quality as compared with the SiO₂ film as deposited, particularly at the sidewalls of the holes. In the above, by additionally feeding N₂ at 1 sccm to the reaction chamber for plasma treatment deposition, a further reduction of hydrogen impurities can be realized.

Example 10 (Prophetic)

In this example, a SiO₂ film is deposited by PEALD, transferred to another chamber for reforming treatment (without atmospheric exposure), and then subjected to reforming treatment using a He/H₂ plasma.

A substrate having a diameter of 300 mm with trenches each having an opening width of 100 nm and a depth of 2000 nm is provided. The substrate is loaded in a reaction chamber for deposition, and a SiO₂ film having a thickness of 5 nm is deposited on the substrate in the reaction chamber by PEALD at a substrate temperature of 300° C. using BDMAS (bisdimethylaminosilane) and an O₂ plasma. The substrate with the SiO₂ film is then transferred to a reaction chamber for plasma treatment (while continuously maintaining a vacuum without atmospheric exposure) which is evacuatable to a desired low pressure using a turbomolecular pump and is equipped with parallel plate electrodes. A susceptor is controlled at a temperature of 300° C., and a pressure of the reaction chamber is controlled at 1 Pa using He flowing at a rate of 20 sccm and H₂ flowing at a rate of 25 sccm, and RF power (13.56 MHz) of 2 kW is applied to the electrodes for 3 minutes, thereby exposing the film to a He/H₂ plasma. The resultant SiO₂ film on the substrate has high quality as compared with the SiO₂ film as deposited, particularly at the sidewalls of the trenches. In the above, alternatively, by feeding H₂ at 20 sccm and Ar at 5 sccm to the reaction chamber for plasma treatment deposition, reforming effect at the sidewalls can also be confirmed.

Example 11 (Prophetic)

In this example, an AlN film is deposited by PEALD, transferred to another chamber for reforming treatment (without atmospheric exposure), and then subjected to reforming treatment using a He plasma, and the above processes are repeated.

A substrate having a diameter of 300 mm with trenches each having an opening width of 100 nm and a depth of 2000 nm is provided. The substrate is loaded in a reaction chamber for deposition, and an AlN film having a thickness of 5 nm is deposited on the substrate in the reaction chamber by PEALD at a substrate temperature of 400° C. using TMA (trimethylaluminum) and an NH₃ plasma. The substrate with the AlN film is then transferred to a reaction chamber for plasma treatment (while continuously maintaining a vacuum without atmospheric exposure) which is evacuatable to a desired low pressure using a turbomolecular pump and is equipped with parallel plate electrodes. A pressure of the reaction chamber is controlled at 1 Pa using He flowing at a rate of 25 sccm, and RF power (13.56 MHz) of 2 kW is applied to the electrodes for 2 minutes, thereby exposing the film to a He plasma. The substrate with the treated AlN film is then transferred back to the reaction chamber for deposition to deposit a second AlN film having a thickness of 5 nm thereon. The substrate with the second AlN film is then transferred back to the reaction chamber for plasma treatment to expose the second AlN film to a He plasma for three minutes. The resultant first and second AlN films on the substrate have high quality as compared with the AlN film as deposited, particularly at the sidewalls of the trenches.

Example 12 (Prophetic)

In this example, a bottom portion of a SiO₂ film is selectively kept in a trench. A substrate having a diameter of 300 mm with trenches is provided, which trenches are covered with a SiO₂ film, wherein a bottom portion of the film (having a thickness of 25 nm) is significantly thicker than a top portion (having a thickness of 10 nm) and a sidewall portion (having a thickness of 5 nm) as illustrated in FIG. 15 (A). Such a film profile can be achieved by using gap-fill CVD method or reflow method which is known in the art. Next, the substrate is transferred to a reaction chamber for reforming treatment, where a pressure of the reaction chamber is controlled at 1 Pa using H₂ flowing at a rate of 25 sccm, and RF power (60 MHz) of 4 kW is applied to the electrodes for 2 minutes, thereby exposing the film to a H₂ plasma for five minutes as illustrated in FIG. 15 (B). All the portions of the film are reformed. Next, the substrate is transferred to a chamber for etching, wherein wet etching is conducted by adjusting a duration of wet etching. For example, wet etching is conducted using a DHF (100:1) for two minutes. As a result, only the bottom portion of the film is selectively left as illustrated in FIG. 15 (C). In the reforming treatment, by properly setting plasma conditions, reforming progresses at a lower portion more than at an upper portion of the film, and further, by adjusting plasma power, etc., the thickness of a portion of the film consequently left in the trenches can be adjusted. In this example, a reformed bottom portion of the film can be selectively formed.

It will be understood by those of skill in the art that numerous and various modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention are illustrative only and are not intended to limit the scope of the present invention. 

We claim:
 1. A method of reforming a conformal insulating film deposited on a substrate having a recess pattern constituted by a bottom and sidewalls, comprising: (i) providing the film deposited on the substrate having the recess pattern in an evacuatable reaction chamber, wherein a wet-etching property of a portion of the film deposited on the sidewalls is inferior to that of a portion of the film deposited on a top surface of the substrate; (ii) adjusting a pressure of an atmosphere of the reaction chamber to 10 Pa or less, which atmosphere is constituted by H₂ and/or He without a precursor and without a reactant; and (iii) applying RF power to the atmosphere of the pressure-adjusted reaction chamber to generate a plasma to which the film is exposed, thereby reforming the portion of the film deposited on the sidewalls, without forming a film, to improve the property of the sidewall portion of the film.
 2. The method according to claim 1, wherein the pressure of the atmosphere of the reaction chamber is 2 Pa or less.
 3. The method according to claim 1, wherein in step (iii), RF power is applied at a power of 2 W/cm² or higher relative to the top surface of the substrate.
 4. The method according to claim 1, wherein in step (ii), the atmosphere of the reaction chamber further contains N₂ at a concentration of 1% or less.
 5. The method according to claim 1, wherein in step (i), a pressure of an atmosphere of the reaction chamber is controlled using a dry pump connected to the reaction chamber, and in step (ii), the pressure of the atmosphere of the reaction chamber is controlled using a turbomolecular pump connected to the reaction chamber.
 6. The method according to claim 1, wherein in step (iii), the reforming of the portion of the film is accomplished by removing hydrogen contained in the film as an impurity, using the plasma.
 7. The method according to claim 1, wherein in step (i), the film has a thickness of 10 nm or less.
 8. The method according to claim 1, wherein step (iii) is conducted until the property of the sidewall portion of the film is improved to be substantially equivalent to the property of a portion of the film deposited on the bottom of the recess pattern or a top surface of the substrate.
 9. The method according to claim 1, wherein the property of the film is resistance to wet etching.
 10. The method according to claim 1, wherein the film is an oxide film or nitride film.
 11. The method according to claim 10, wherein the film is selected from the group consisting of SiO₂, SiN, SiOC, SiCN, GeOx, GeN, AlOx, AlN, TiO₂, and TaO₂.
 12. The method according to claim 1, wherein step (i) comprises depositing the film in the reaction chamber by cyclic deposition.
 13. The method according to claim 12, wherein the film is deposited by one cycle or multiple cycles of the cyclic deposition.
 14. The method according to claim 13, wherein the cyclic deposition is plasma-enhanced atomic layer deposition (PEALD).
 15. The method according to claim 13, wherein steps (i) through (iii) are repeated.
 16. The method according to claim 1, further comprising, between steps (i) and (ii), evacuating the reaction chamber to reduce the pressure to less than the pressure used in step (ii).
 17. The method according to claim 1, wherein in step (ii), the atmosphere contains no gas other than H₂, He, and N₂.
 18. The method according to claim 17, wherein the atmosphere consists of H₂.
 19. The method according to claim 1, wherein the recess pattern is constituted by trenches having a width of 20 nm to 100 nm and an aspect ratio of 2 to
 10. 20. The method according to claim 1, wherein in step (iii), RF power is applied to an upper electrode which is capacitively coupled with a lower electrode on which the substrate is placed.
 21. The method according to claim 1, wherein in step (i), a portion of the film deposited on the bottom of the recess pattern is thicker than the portion at the sidewalls of the recess pattern and the portion at the top surface of the substrate. 